The object of this study is to increase the accuracy of karyotype analysis and related studies by developing specific immunochemical probes which will permit the recognition of individual chromosome bands in human and other genomes, even if the chromosomes have undergone rearrangements. Specifically purified antibodies to nucleosides and oligonucleotides, which react with single-stranded but not native DNA, will be used. Selective denaturation of the DNA in fixed chromosomes will be brought about by chemical, photochemical and enzymatic methods and the locations of extensive antibody binding will be detected by immunofluorescence or immunoperoxidase techniques. Mammalian mitotic and meiotic chromosomes as well as Dipteran polytene chromosomes will be used in the development and testing of these methods. The development of additional antibody probes will make it possible to characterize structural changes involving certain chromosomes, which will facilitate evolutionary studies. More important, the methods will have immediate clinical applicability in recognition and characterization of human chromosome abnormalities.